UCLA scientists last year made a dramatic breakthrough in solar power tech when they developed solar cells that can both generate electricity and also let visible light through, meaning they could turn ordinary windows and screens into power sources. Just a year later, the team achieved something even more impressive: It just about doubled the efficiency of the cells’ power generation.

Where the initial polymer film solar cells converted about 4% of the energy that hit them into power, the new cells manage close to 8% efficiency. They’re double-layered polymers, sandwiching an additional see-through layer that stops the system from losing too much energy. The team imagines when the technology is commercialized, it will offer a cheap and simple way to convert office or home windows into electrical power sources. Someday soon this sort of tech could also mean your smartphone or tablet gently tops off its battery when its screen hits the light.

Harnessing green energy in this way is a neat compromise, and there are other ways to do so: Apple has patented an “in-cell” system where the electronics for converting light into electricity are actually embedded into the display alongside the systems used to make your phone’s screen light up in color.